A huge variety of sensors have been used in large numbers in our everyday life for some time. They are specialized for particular purposes including detection of car thefts, house break-ins, and fires. These sensors typically make up sensor networks for individual purposes. A sensor network system made up of these sensor networks is capable of collectively managing various kinds of sensor information.
Each sensor network has a sensor network controller connected to the sensors by a wired or wireless communicable link. Therefore, results of detection by sensors and other sensor information are communicated by the sensor network controller.
In addition, the sensor network system has a server computer (“server”) which collectively manages information from the sensor networks. The server has communicable connections with the sensor network controllers of the sensor networks so that the server can acquire sensor-originated information via the sensor network controllers. Also, the server is capable of controlling operation of the sensors.
Many sensor networks cover a large geographic area. The server is therefore connected to the sensor network controllers over a communications infrastructure providing long distance communications. An example of such communications infrastructure is a relay network interconnecting multiple relays.
In sensor network systems like this one, sensors are installed at various places. Some sensors need to be installed where they cannot rely on an external power supply, in which case the sensor should operate from a battery.
If one of battery-driven sensors in a system runs out of battery power, a maintenance work is required to recharge the sensor. The sensors vary in battery capacity and power consumption, therefore running out of battery power at different times from sensor to sensor. Under these circumstances, the batteries must be frequently recharged, which adds to the maintenance workload for the sensor network system manager.
Data travels via vastly differing routes in a relay network, depending on the positional relationship of the server and the sensor network controllers transferring the data to and from the server. Besides, each relay is communicable with one or more relays; data can travel between the server and a given sensor network controller via various routes.
In such systems, a particular relay may be used extremely frequently, depending on how the communications route is selected. If the relay is driven by a battery, it quickly consumes battery power and calls for frequent recharging of the battery. This means added frequency of maintenance recharging and an added workload for the sensor network system manager. Another problem is that an extremely frequent use of a relay shortens the service life of the relay and its battery.
The present invention, made to address these issues, has an objective to offer a sensor network system managing method and a relay network managing method which, in a sensor network system in which multiple sensors are connected over a relay network or other communications network to a server collectively managing the sensors, reduce the maintenance workload for the system manager, especially, in the recharging of sensor and relay batteries.